<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>类选择器</title>
</head>
<style>
    .red {
        color: red;
        /*font-size: 20px;*/
    }
</style>
<body>
<ui>
    <li class="red">苹果</li>
    <li class="red">香蕉</li>
    <li>草莓</li>
</ui>
<div class="red">我是什么？</div>
</body>
</html>